Researchers from the City University of Hong Kong (CityU), in collaboration with other institutions, have developed a highly efficient artificial photocatalytic system that surpasses natural photosynthesis in converting carbon dioxide into methane, a valuable fuel, using light. This innovative system offers promising potential for contributing to the goal of carbon neutrality.
Traditional attempts at artificial photosynthesis have encountered challenges due to the degradation of photosensitizers or catalysts in water. However, the joint research team devised a solution by employing a supramolecular assembly approach inspired by the light-harvesting chromatophores found in purple bacteria. These bacteria demonstrate exceptional energy transfer efficiency from sunlight. At the core of this novel artificial photosynthetic system lies a stable artificial nanomicelle, a polymer that assembles in water. The nanomicelle features a hydrophilic head that functions as a photosensitizer to capture sunlight, and a hydrophobic tail that prompts self-assembly in water. When combined with a cobalt catalyst, this assembly leads to photocatalytic hydrogen production and carbon dioxide reduction, resulting in the generation of hydrogen and methane.
Through advanced imaging techniques and ultrafast spectroscopy, the researchers unraveled the atomic details of the innovative photosensitizer. The unique structure of the nanomicelle's hydrophilic head, combined with hydrogen bonding between water molecules and the nanomicelle's tail, yielded a stable and water-compatible artificial photosensitizer. This innovative design overcame the instability and water-incompatibility issues commonly faced in artificial photosynthesis. The electrostatic interaction between the photosensitizer and the cobalt catalyst, along with the strong light-harvesting antenna effect of the nanomicelle, enhanced the photocatalytic process.
In experimental trials, the artificial photocatalytic system demonstrated impressive results. Over a 24-hour period, the methane production rate exceeded 13,000 μmol h−1 g−1, with a quantum yield of 5.6%. Moreover, the system achieved an efficient solar-to-fuel efficiency rate of 15%, surpassing the efficiency of natural photosynthesis. A notable advantage of this system is its economic viability and sustainability, as it avoids the use of expensive precious metals. The team's hierarchical self-assembly approach relies on readily available elements like zinc and cobalt porphyrin complexes, ensuring cost-effective implementation. Professor Ye Ruquan, an associate professor at CityU, believes that this breakthrough discovery will significantly impact the design of future photocatalytic systems for carbon dioxide conversion and reduction using solar energy. This advancement aligns with the pursuit of carbon neutrality and offers a promising pathway to harnessing solar energy for efficient and environmentally friendly fuel production.
The research received support from various funding sources, including the National Natural Science Foundation of China, the Guangdong Basic and Applied Basic Research Fund, the Shenzhen Science and Technology Program, and the Hong Kong Research Grant Council.
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